Transgenic fish will be used to study the effect of pesticides upon gene expression of transgenic reporter genes that report changes in the estrogen-responsive, retinoic acid-responsive pathways in developing fish and in the development of the nervous system. Our hypothesis are: 1) Liver reporter transgenic fish embryos and larvae can be used as biosensors to detect whole organism effects of environmental toxicants. 2) There may be unique windows of sensitivity of chemicals which impact upon the estrogen receptor signal transduction pathway that can be detected and evaluated in fish models. 3) Dicistronic reporter genes will allow for both tissue specific expression studies plus quantitative evaluation of toxicants upon whole fish embryos. 4) Transgenic techniques developed for the zebrafish can be used for indigenous species such as the killifish, Fundulus heteroclitus. The specific aims of this proposal are: I. To explore the use of transgenic zebrafish models to screen several superfund chemicals for detectable differences of GFP expression. II. To examine the behavior and incorporation of the GFP positive primordial germ cells into the developing reproductive tract and to see if there are biological effects upon sexual determination of the fish through treatment with pesticides investigated in specific aim I. III. To develop dicistronic vectors for the appropriate transgenic promoters that will allow for ligand inducible expression of both a luciferase gene (for quantitative measurement) and a GFP gene (for anatomical localization of signal). IV. To develop Fundulus models with the most appropriate transgenes based upon the results of specific aims I and II.